The neuronal adaptor protein X11alpha/mint-1 interacts with amyloid precursor protein (APP) to regulate its trafficking and processing in vitro. In transfected non-neuronal cells, X11alpha inhibits alpha- and gamma- but not beta- cleavage of APP. Because the phosphotyrosine binding (PTB) domain of X11alpha interacts specifically with the APP family, X11alpha appears to inhibit gamma-cleavage of APP specifically while sparing gamma-cleavage of Notch and other substrates of regulated intramembranous proteolysis. To determine the in vivo significance of these in vitro data, we will generate and characterize novel hX11alpha transgenic mice and X11alpha knockout mice and examine murine APP metabolism. Crosses of these mice to Tg2576 mice (transgenic for the Swedish mutation of hAPP, or hAPPswe) will probe the effects of XI la on hAPPswe metabolism and on the development of partial AD-like phenotypes in aging brain. A recent human genome-wide analysis revealed significant linkage of sporadic AD to single nucleotide polymorphisms (SNPs) on chromosome 9, perhaps including the X11alpha region. We will probe genetic linkage of SNPs in the X11alpha region to sporadic AD by using genomic DNA extracted from samples from AD subjects versus carefully-matched control subjects. The specific aims are to: 1) generate X11alpha knockout and hX11alpha transgenic mice and determine effects on murine APP metabolism in brain and in primary neuronal cultures, 2) cross X11alpha knockout and hX11alpha transgenic mice with Tg2576 mice to determine a) modulatory effects on hAPPswe metabolism in brain and in neuronal cultures, and b) development of AD-like phenotypes with aging, and 3) elucidate the SNPs and haplotypes within or adjacent to the X11alpha gene of AD cases and age-, gender-, and ApoE-matched controls to determine if there is a statistically significant link to sporadic AD. Specific aim 3 will study DNA samples obtained from the Pathology Core and from other ADRCs. These results will 1) inform the normal functions of X11alpha as well as APP and its derivatives in CNS neurons, 2) lay the groundwork for viral-vector based gene therapy of AD using either X11alpha or its PTB domain in hAPP transgenic mouse models, and 3) probe a potential genetic risk factor of sporadic AD.